© 2012 delmar, cengage learning cooling system service chapter 21

© 2012 Delmar, Cengage Learning

Cooling System Service

Chapter 21


Objectives• Diagnose cooling system problems• Service all parts of the cooling system


Introduction• Cooling systems are dependable

– Require periodic maintenance

• Coolant system service– Best value in terms of preventative maintenance

• Working on cooling systems is not difficult– Sometimes very profitable


Diagnosing Cooling System Problems

• Causes of cooling system problems:– Coolant level

– Restricted radiator

– Stuck thermostat

– Defective water pump

– Fan shroud

– Frozen coolant

– Defective cooling fan

– Exhaust blockage

– Inoperative EGR valve


Radiator Cap• Damaged cap allows pressure to escape

– Boiling point may drop causing boil over

– Pressure tester tests the cap’s pressure valve

• Radiator inspection – Inspect for leaks, damage, and obstructions

• Coolant should fill entire radiator opening as it flows• Check condition of fins by rubbing gently• Broken engine mount can cause excessive

movement• Leaks from heat exchanger cause transmission fluid

to be pumped into radiator


Coolant Service• Coolant loses protective ability and becomes

corrosive– Check cold coolant for grease, dirt, rust, and

corrosion bloom

– Electrolysis makes small holes in parts• Cooling conductivity is checked with voltmeter• Voltmeter reading should be less than 0.4• Also caused by poor electrical conductivity in

ground circuit

– Coolant should be changed every 30,000 miles

– Most radiators have plastic drain valves


Coolant Service (cont'd.)• Special tools are used to separate a stuck hose

from the radiator• Flush the system

– Dirt and minerals build up in water jackets


Coolant Service (cont'd.)• Airlift leak check and airlock

purge– Venturi system: uses

compressed air to create a vacuum in the cooling system

• Effective way to check for leaks and refill the cooling system


Coolant Service (cont'd.)• Coolant exchanger: prevents spillage• Aluminum oxide: forms when coolant is over

diluted


Testing Coolant Conditionand Strength

• Coolant test strips – Test the condition of the coolant

• Coolant alkalinity (pH)– Coolant must continue to contain reserve alkalinity

• Coolant density testers– Measure a coolant’s freeze point

• Hydrometers and refractometers – Test coolant concentration

• Several coolant types– DexCool and HOAT coolant


Thermostat Service• Test in the vehicle

– Hand-held multimeter or putting it into coolant

• Thermostat check after removal– Lower into hot water with a thermometer

• Good thermostats: fully closed when cold and fully open near its rating

– When removing: drain until level is below thermostat housing first

– When replacing: be sure the thermostat fits into the groove in the block or outlet housing

• Bleed air from the system to prevent overheating


Locating Leaks• Locate leaks before starting a repair

– Pressure tester identifies internal or external leaks– Test engine at different temperatures


External Leaks• Check for external leaks:

– Heater core and hoses

– Radiator hoses

– Thermostat housing and core plugs

– Radiator and coolant pump

• Core plug inspection – Common: rust and leakage

• Coolant outlet (thermostat) housing inspection– Inspect for leaks or damage


Internal Leaks• Bubble test

– Look for bubbles in radiator when engine is warm

• Hydrostatic lock– Engine stops with a piston down with valves

closed and crankshaft will not turn

• Block check test– Samples air in the radiator filler neck

– Carbon monoxide changes the color of the tester

• Infrared analyzer – Checks for exhaust gas in the coolant


Recovery Tank Service• Most cooling systems have a plastic coolant

reservoir or recovery tank– Recycles the coolant

– Helps decrease corrosion

• During a cooling system flush– Recovery tank or auxiliary reservoir is flushed of

contaminants


Cooling System Repairs• Replacing core plugs

– Pound it sideways with a blunt drift punch

– Do not leave an old core plug inside the block

• Core plug installation– Clean the block opening with an emery cloth

– Apply sealer to sides of new plug

– Pound in with a driver or socket that fits loosely into the inside diameter of plug


Water Pump Service• Coolant pump leakage: visible from vent hole• Worn bearing: use a stethoscope to listen for

bad bearing• Worn or broken impeller: indicated with water

pump action in radiator of warm, running engine• Water pump replacement: before installing,

remove all fasteners– Inspect the old pump, select a new one, install,

and refill


Fan Inspection• Out-of-balance fan assembly leads to cooling

pump shaft and bearing failure• Possible sources of pump failure

– Leaking fan clutch

– Bent or broken fan

– Cocked or cracked aluminum fan spacer

• Clean all mating surfaces and tighten fan bolts evenly to avoid cocked assembly

• Fan clutch inspection– Fluid leaks and see if it is loose or frozen


Electric Cooling Fan Service• Electric fans respond to signal from coolant

temperature switch– Check for disconnected wire or burned out fuse

• Inspection– Ohmmeter reads across the switch terminals

• Should indicate infinite resistance

– Wires connected: fan should engage when engine is warm

– Wires disconnect: ohmmeter should indicate no connectivity


Heater Core Service• Heater core

– May leak or become plugged

– Supplied with engine coolant through two hoses

– Heat demands: controlled by doors to ducts around heater core

• Hybrids cooling systems– Powered by electric motors that do not produce

heat when the engine is shut off• Coolant system does not have to deal with heat

load

© 2012 delmar, cengage learning cooling system service chapter 21

Documents

coolant exchanger

hoat coolant slide

cengage learning slide

obstructions coolant

cooling system slide

coolant thermostat check

radiator slide

coolant types dexcool